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Sept. 10, 1963 w. A. MORGAN AUTOMATIC COMPUTER FOR USE WITH MASS SPECTROMETERS Filed Nov. 24, 1961 ATTORNEY.

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where M=mass to charge ratio of United States Patent O 3,103,582 AUTOMATIC COMPUTER FOR USE WITH MASS SPECTROMETERS Walter A. Morgan, Baytown, Tex., assignor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, NJL, a corporation of Delaware Filed Nov. 24, 1961, Ser. No. 154,591 3 Claims. (Cl. 235-494) This invention relates to computers in general and more particularly to a system for use with a mass spectrometer.

One method of determining the chemical or elemental composition of a material as Well as the relative abun dances of the various materials in the sarnple is by means of a mass spectrometer. In a mass spectrometer, the material to be analyzed is ionized, accelerated by an electrostatic field and resolved into homogeneous ion beams by means of a magnetic field. Each homogeneous beam contains ions having a single mass to charge ratio. By varying the strength of the electrostatic field used to accelerate the ionized particles, ion beams of various mass to charge ratio can be brought to focus on the ion collector and their relative intensities determined.

There has long been a need for automatically determining the mass to charge ratio of the ions brought to focus at the collector of a mass spectrometer under varyingconditions of accelerating voltage and magnetic field strength. The invention to be described herein satisfies this long-felt need. The invention automatically and continuously measures the ion acceleration voltage and the magnetic field strength in the mass analyzer section of the spectrometer and produces an output voltage directly proportional to the mass to charge ratio of the ions brought to focus at the collector.

A better understanding of the invention, as well as its many advantages, may be had by reference to the following detailed description and single FIGURE which is a diagram of a simplified mass spectrometer equipped with the computing system of myinvention.

Referring to the drawing, a mass spectrometer is shown including an analyzer a The material to be analyzed, such as a gaseous hydrocarbon, is admitted into the ionization chamber 12 by means of an inlet, such as gas inlet 13. The gaseous molecules in ionization chamber 12 are ionized in the ionization chamber 12. 7 An electrostatic field impressing electrical circuit is provided for accelerating the ionized particles through exit slit 14. This circuit includes a variable D.C. voltage source .15 which feeds a voltage through lines 16 and 17 to apply a dilference in potential V between the chamber 12 and accelerating electrode 18.

After the ionized particles have accelerated, they are resolved into separate homogeneous beams according to their mass to charge ratio by means of a magnetic field produced between the poles of an electromagnet (not shown). Those ions which pass through the slit 19 impinge on the collector electrode 20. The current produced by the ions impinging on the collector electrode 20 is measured by a recording apparatusZl.

The equation, which describes the ion optics of a mass spectrometer such as that shown in the figure is:

the ions brought to focus at the collector V=the ion accelerating voltage B=the magnetic field strength in gauss r=the radius of curvature in centimeters 3,103,582 Patented Sept.'10 1963 Since for a given mass spectrometer the radius of curvature r is fixed once the spectrometer is constructed, the above Equation 1 can be expressed as:

The remainder of the electrical system shown in the figure is used to solve Equation 2 and produce an output voltage proportional tothe mass to charge ratio of the ions impinging upon electrode 20.

The resistor R and the resistor R form a voltage divider connected across the ion accelerating voltage supply 15. A voltage v proportional to the ion accelerating voltage V is obtained across resistor R where K; is a constant Substituting Equation 5 in Equation 4 and solving for i yields:

Since the gain G of amplifier A can be made very large, G1R3 1 and -i-GlRg G Rg.

Therefore:

Transducer T is what is known as a Hall efiect transducer. This transducer is made from a semiconductor material such as indium arsenide. When such a material is placed in a magnetic field and a current is made to flow through the semiconductor in a direction perpendicular to a magnetic field, a voltage is produced across the semiconductor along an axis normal to both the magnetic field and the direction of current fiow. The equation describring this effect is:

where 1) ial E =KiB E =the output voltage from the transducer in volts i =the current uthrough the transducer in amps. B=the magnetic field strength in gauss K=a proportionality constant with the units volts per amp. per gauss I The output current, i from a second amplifier A is equal to:

( 2= 2( R4 T1 V where E is a constant potential obtained from a tap 23 in contact with the resistor R connected across a battery 24 to form a potentiometer.

(1 r i l i The output current, i from amplifier A is fed through line 25 to a solenoid 26. This solenoid may be an air core solenoid. The magnetic flux B is produced by the current, i passing through the windings of the air core solenoid 26. The solenoid 26 is in close proximity to transducer T so that the magnetic flux produced by the solenoid passes through transducer T Therefore:

where B =the magnetic field strength in gauss at T i =the current through coil 26 in amps.

K =a proportionality constant with the units gauss per amp.

Combining Equations and 11:

Substituting Equation 12 in 9 and solving for i Since the gain G of amplifier A can be made very large, G 1 1K i1 1 and l-l-GzKlK i GzK K i Therefore:

E34 (14 Substituting Equations 3 and 7 in 14:

R3ER4 W From an examination of Equation 15, it can be seen that the current, i through line and coil 26 is inversely proportional to the ion accelerating voltage V.

The current, i is fed through the coil 26 to a second Hall efiect transducer T A difierential amplifier A is connected between the transducer T andHall effect transducer T A resistor R is connected in the output of the differential amplifier A A feedback circuit consisting of lines 27 and 28 connected across resistor R is used to conduct the voltage across the resistor R back to the difierential amplifier A The output current, i from the differential amplifier A is conducted through line 29 to the transducer T The current in line 29 which flows through transducer T is:

Substituting Equations 17 and 18 in 16 and solving for i yields:

7: G3Kgi2 B2 l+G3R Since the gain G of amplifier A can be made very Now the Hall effect transducers T and T are mounted between the pole faces of the mass spectrometer analyzer magnet and in close proximity to each other and the analyzer section of the mass spectrometer tube.

Therefore:

B2:B3=B

Substituting Equations 15 and 23 in 22 yields:

R lf KsEiq 24) r m v R3Z(2K3ER4 25) Defini g kl m B2 (26) a (V) Dividing Equation 2J6 by 2 yields:

where E =output voltage from the computer M=mass to lcharge ratio of the ions brought to focus at the collector Thus, this computing system which is primarily for use With a mass spectrometer automatically produces a voltage E which is proportional to the mass to charge ratio of the ions brought to focus at the collector 20. The voltage E ,can be measured with a recorder 30 or digital voltmeter.

It is obvious that the computing system shown herein has applicability for computing operations other than in the mass spectrometer system shown. For example, a variable function Y can be multiplied by a second variable Z, with the product [divided by a third variable X. This could be done by providing a voltage across resistor R proportional in magnitude to X. The magnet power supply 31 can be removed. Then a current proportional in magnitude to Y can be fed to coil 32 and a current proportional to Z fed to coil 33.

The voltage fed to the recorder 30 would then be equal 1. A computer for dividing a first variable by a second variable comprising: means for obtaining a first current =a constant proportional to the magnitude of the second variable;

means responsive to said first current for obtaining a second [current inversely proportional to the second variable and including a solenoid, and a first Hall effect transducer in close proximity to said solenoid, said first current being fed through the first Hall effect transducer and said second current being fed through said solenoid; and means for obtaining a voltage proportional to the first variable divided by the second variable including a secondHall effect transducer connected to said solenoid, and a mangetic fiux generating member for generating a magnetic flux proportional to the magnitude of said first variable, said second Hall effect transducer being in close proximity to the magnetic flux generating member.

2. A computer in accordance with claim 1 wherein said proportional to the first variable including a first Hall eifect transducer and a first magnetic flux generating member in close proximity to said first Hall effect transducer, said first magnetic lflIl-X generating member being adapted to generate a fiux proportional to the magnitude of the first variable; a second Hall effect transducer and a second magnetic fiux generating member in close proximity to said second Hall efiect transducer, said second magnetic flux generating member being adapted to generate a flux proportional to the magnitude of the second variable; a differential amplifier electrically connected between said first and second Hall effect transducers; a resistor in the output of the differential amplifier and a feedback circuit for [feeding the voltage across the resistor in said difierential amplifier circuit back to the differential amplifier, the output of said differential ampliifier being fed to said second Hall effect transducer.

References Cited in the file of this patent UNITED STATES PATENTS 2,969,462 Morgan Jan. 24, 1961 

1. A COMPUTER FOR DIVIDING A FIRST VARIABLE BY A SECOND VARIABLE COMPRISING: MEANS FOR OBTAINING A FIRST CURRENT PROPORTIONAL TO THE MAGNITUDE OF THE SECOND VARIABLE; MEANS RESPONSIVE TO SAID FIRST CURRENT FOR OBTAINING A SECOND CURRENT INVERSELY PROPORTIONAL TO THE SECOND VARIABLE AND INCLUDING A SOLENOID, AND A FIRST HALL EFFECT TRANSDUCER IN CLOSE PROXIMITY TO SAID SOLENOID, SAID FIRST CURRENT BEING FED THROUGH THE FIRST HALL EFFECT TRANSDUCER AND SAID SECOND CURRENT BEING FED THROUGH SAID SOLENOID; AND MEANS FOR OBTAINING A VOLTAGE PROPORTIONAL TO THE FIRST VARIABLE DIVIDED BY THE SECOND VARIABLE INCLUDING A SECOND HALL EFFECT TRANSDUCER CONNECTED TO SAID SOLENOID, AND A MANGETIC FLUX GENERATING MEMBER FOR GENERATING A MAGNETIC FLUX PROPORTIONAL TO THE MAGNITUDE OF SAID FIRST VARIABLE, SAID SECOND HALL EFFECT TRANSDUCER BEING IN CLOSE PROXIMITY TO THE MAGNETIC FLUX GENERATING MEMBER. 